1. Field of the Invention
The present invention relates to a method of manufacturing a three dimensional image display device.
2. Description of the Related Art
Flat panel display devices are generally used as display panels for three dimensional image display devices. Such flat panel display devices include: a liquid crystal display panel (LCD) which controls the intensity of light by utilizing the orientation of liquid crystals, a plasma display panel (PDP) in which ultraviolet rays of plasma discharges cause phosphors to emit light, a field emission display panel (FED) in which electron beams of a field emission electron emitter cause phosphors to emit light, and an electron emission display panel in which electron beams of a surface-conduction electron emitter cause phosphors to emit light.
Various systems such as a multi-view system and an integral imaging system are used as three dimensional image display systems for three dimensional image display devices. As one type of three dimensional image display devices which display three dimensional images using such systems, there has been developed a three dimensional image display device including a lenticular lens. Three dimensional images provided by the display device including a lenticular lens are viewable without use of glasses or the like for three dimensional image viewing.
In order to mount a lenticular lens on a display panel, an adhesive applied on the display panel in a rectangular frame shape is used to bond a lens plate including the lenticular lens and the display panel together. In this regard, a technique of mounting a lenticular lens on a liquid crystal display panel has been proposed for the purpose of improving the efficiency for light utilization (see JP-B No. 3708112, for example).
In a process of mounting a lenticular lens on a display panel, it is so difficult to bring the lenticular lens into complete contact with the display panel that a gap may be formed therebetween. Even when a display panel and a lenticular lens are brought into complete contact with each other, deformation due to their own weights, partial pressurization from outside, ambient temperature rise and the like may cause a gap after the manufacturing. If such a gap is larger than an allowable range (for example, a range of a desired value plus or minus several tens of μm), an error in the viewing angle falls outside an allowable range. Accordingly, the display quality of a three dimensional image is degraded.
One possible countermeasure for solving the above problem is a method in which, by using an adhesive member in a continuous frame shape (close-loop shape), a display panel and a lens plate are bonded together in a reduced pressure atmosphere with the display panel and a lenticular lens facing each other. This method, however, causes a phenomenon in which an internal pressure in an enclosed space in the display device becomes higher than a pressure in the reduced pressure atmosphere in which the bonding is performed. This phenomenon is explained in detail below.
In the process of manufacturing the display device, the height of an adhesive applied on a periphery portion of a display panel is made higher than the height of the final adhesive (adhesive layer) after the manufacturing. Such application of the adhesive is intended to ensure bonding in the entire adhesive-applied area after the bonding is completed. With such application of the adhesive, however, the applied adhesive is squashed to some extent by the display panel and the lens plate before the display panel and the lens plate are bonded finally. In this bonding process, when the display panel and the lens plate come close to each other with the adhesive member interposed therebetween, the display panel and the lenticular lens firstly form an enclosed space while being spaced apart from each other. Thereafter, as the display panel and the lens plate come closer to each other, the volume of the enclosed space proportionally decreases. As a result, the internal pressure in the enclosed space becomes higher than the ambient pressure (bonding pressure) of the surroundings.
Here, when Vb denotes the volume of the enclosed space formed in a distant state where the display panel and the lenticular lens are spaced apart from each other; Va denotes the volume of the enclosed space in a bonding complete state where the bonding is completed; and Pb denotes the ambient pressure of the surroundings (bonding pressure) where the bonding is performed, a final internal pressure Pa in the enclosed space is expressed as Pa=Pb×Vb/Va. For example, when Pb=0.5 atm and Vb/Va=1.5, Pa=0.75 atm.
In the case where the adhesive is applied to the display panel or the lens plate in a close-loop shape in advance to bond the display panel and the lens plate together, the volume Vb of the enclosed space in the distant state is determined by the lens shape, the frame size and the height of the adhesive applied in the close-loop shape, and the like. Even under the same conditions (pressure, nozzle diameter, application speed, and the like) of an applicator, the height of the applied adhesive (simply called “application height” below), in particular, varies depending on a viscosity change of the adhesive due to a temperature, a time length from the completion of application to bonding, or the like. Such a variation in the application height largely affects the final internal pressure Pa.
As described above, the internal pressure Pa of the enclosed space is higher than the ambient pressure (bonding pressure) Pb of the atmosphere where the bonding is performed. As a result, the internal pressure Pa only has a small pressure difference from the atmospheric pressure. This condition facilitates the generation of a gap between the display panel and the lens plate because of deformation due to their own weights, partial pressurization from outside, ambient temperature rise and the like, and thereby makes it difficult to maintain accuracy of a gap between the display panel and the lens plate, i.e., gap accuracy between the pixels and the lens.